Wolfgang Baehr, PhD

BASIC RESEARCH PROJECT

Dr. Baehr’s Research Project

The road to understanding INPP5E-Joubert Syndrome

Current Research Interests

Retinitis pigmentosa (RP), Leber congenital amaurosis (LCA) and cone-rod dystrophies (CRD) are devastating diseases for which no cures exist. In RP, central visual acuity and cone function are often preserved until late in the disease course; however, patients with end-stage disease have no light perception at all. LCA is even more severe where both rod and cone photoreceptors degenerate early in life, and children are often born blind. We are interested in understanding mechanisms leading to retina disease and in developing gene-based therapies to address photoreceptor degeneration.

This application studies the role of INPP5E, a phosphoinositide phosphatase present in photoreceptors, in pathogenesis of ciliated cells. A cilium is an antenna-like protrusion common to most mammalian cells, including photoreceptors (“outer segments”). Cilia are important for cell-to-cell communication during tissue development. INPP5E mutations are associated with Joubert syndrome, a syndromic ciliopathy. Common features of Joubert syndrome include ataxia (lack of muscle control), hyperpnea (abnormal breathing patterns), abnormal eye and tongue movements, polydactyly (more than ten digits) and retinitis pigmentosa. We propose to study the consequences of INPP5E deletion specifically in retina photoreceptors, and devise gene-based therapies to ameliorate or cure disease.

Progress in 2017

We hypothesize that INPP5E, immunolocalized in the rod Golgi apparatus, is required for membrane vesicle trafficking and ciliogenesis. As immunolocalization of INPP5E to the Golgi is controversial, we generated an EGFP-INPP5E expression construct to avoid misinterpretation of INPP5E localization due to antibody artifact. Neonatal electroporation of the construct and colabeling with a Golgi marker (anti-giantin) demonstrates that INPP5E distributes to peri-nuclear endoplasmic reticulum and Golgi apparatus, and is excluded from WT and mutant outer segments. Thus, farnesylated INPP5E traffics to the Golgi, most likely bound to the prenyl-binding protein PDE6δ, and is retained in this subcellular compartment.

Plans for 2018

Specific Aims:
Because germline knockouts of INPP5E are lethal, we propose to generate photoreceptor- and retina-specific deletions of INPP5E (Aim 1). The knockout mouse will allow us to pinpoint onset of degeneration during postnatal development and analyze trafficking failures. The photoreceptor-specific knockout may allow mechanistic interpretation of other INPP5E-deficient primary cilia.

In aim 2, we will prepare selfcomplementary AAV vectors for gene replacement therapy in the knockout mouse; this mutant mouse will be critical to study the molecular mechanisms underlying retina degeneration in Joubert syndrome with the intent to design therapy.

Dr. Baehr with his lab group

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Mission of RRF

The mission of the Retina Research Foundation is to reduce retinal blindness worldwide by funding programs in research and education. As a public charity, RRF raises funds from the private sector and the investment of its endowment funds.